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Abstract

Detection of glucose in water solution for several different concentrations has been performed with the purpose to determine the sensitivity of Near Infrared Bloch Surface Waves (λ = 1.55μm) upon refractive index variations of the outer medium. TE-polarized electromagnetic surface waves are excited by a prism on a silicon nitride multilayer, according to the Kretschmann configuration. The real-time reflectance changes induced by discrete variations in glucose concentration has been revealed and analyzed. Without using any particular averaging strategy during the measurements, we pushed the device detection limit down to a glucose concentration of 2.5mg/dL, corresponding to a minimum detectable refractive index variation of the water solution as low as 3.8·10−6.

Figures (3)

Experimental setup for BSW coupling in the Kretschmann configuration. The illumination beam has low divergence (~0.038 deg.) and a linear polarization parallel to the 1DPC interfaces (TE). A flow cell is contacted to the top surface of the 1DPC.

(a) Best-fit of the spectrally resolved reflectance profiles R(λ) at fixed angle θ0 showing the red-shift of the BSW resonance for increasing glucose concentrations. For the sake of clarity, the experimental points are shown only for the three largest concentrations. (b) Spectral shift Δλ of the BSW resonance as a function of the glucose concentration C and of the corresponding refractive index variation of the solution. The linear fit of the experimental data (solid, red on-line) and the calculated Δλ (dashed, blue on-line) are shown for comparison.

Measured reflectance variations ΔR(t) as a function of the glucose concentration C in water solution. Insets: temporal ΔR(t) traces recorded during sequential injection cycles water/glucose solution/water for the two concentrations corresponding to the indicated experimental points. The continuous line shows the best linear fit of the experimental data.